1. Field of the Invention
The present invention relates to an apparatus and a method of emulating a disk drive memory storage device.
2. State of the Art
One of the present trends in computing is toward increasing miniaturization of computers and computing devices. Laptop, notebook and palmtop computers represent the fastest growing market segment in the computer market. Particularly with regard to laptop and notebook computers, the demand for mass storage devices for such computers, coupled with the space constraints inherent in building these machines, has resulted in the "form factor" of disk drives being reduced from 51/4 inch to 31/2 inch and now down to 21/2 inch. The projected trend is from 21/2 inch form factor disk drives prevalent today toward sub-two-inch drives in 1994 and sub-one-inch drives in 1997.
As the form factor of disk drives becomes smaller, a multitude of serious problems may be expected to be encountered. Small disk plating techniques exhibit very low production yields. Since very low-flying heads or even contact-recording heads are required due to low linear disk speed and higher bit densities, contact of the head with the disk can cause "head slapping", resulting in higher shock requirements and excessive disk wear. Low-yield thin-film heads or vertical-recording-technology heads are required, as are small bearings or ceramics for the necessary motors and actuators. Signal-to-noise ratios will be significantly decreased, forcing the user to tolerate higher error rates and possible data loss. To accentuate the foregoing difficulties, hard disk suppliers are becoming fewer. As a result, the magnetic hard disk found in high-volume notebook PCs is expected to become difficult to purchase due to difficulty on the part of the hard disk manufacturer of supplying quality merchandise that can be produced with economical yields.
In contrast to the foregoing situation, solid-state semiconductor memories, in particular DRAMs, are presently in abundant supply at relatively low cost. In this respect, DRAMs represent an attractive alternative to small-form-factor disk drives for mass memory storage. Using DRAMs, memory performance may be increased by a factor of several times over a comparable hard drives. Unfortunately, however, DRAMs continually consume power, a scarce commodity in notebook applications. Solid-state RAM disks are known, as disclosed for example in U.S. Pat. No. 5,077,737, incorporated herein by reference. In general, the RAM disk of the foregoing patent is not designed for maximum power efficiency but is designed instead to utilize inexpensive "off-spec" DRAM chips. Other RAM disks are disclosed in U.S. Pat. Nos. 4,780,808 and 4,896,262.
A need therefore exists for curtailing the power consumption of DRAMs so that they may be used for mass memory storage in notebook applications. The present invention relates to a power efficient RAM disk and a method of emulating a rotating memory device.